The invention relates to a method in connection with a roof drainage apparatus, in which a water flow, when increasing, is changed from an open flow into a closed flow and directed into a water-outlet tube through an opening arranged in the bottom of a trough recessed in a roof structure. The invention also relates to a roof drainage apparatus.
Such solutions are well-known at present. As an example of prior art solutions can be mentioned an apparatus disclosed in Finnish Patent 70446. In this known solution the opening is arranged directly in the roof level. The means changing open flow into closed flow comprise a plate positioned above the opening, the size of the plate and its distance from the roof level being dimensioned according to criteria causing closed flow.
Another example of a prior art solution is an apparatus disclosed in Finnish Patent 75394. This apparatus utilizes the same basic principle causing closed flow as the apparatus according to Finnish Patent 70446. However, in the apparatus according to Finnish Patent 75394, the opening is arranged in a trough recessed in the roof structure and not directly in the roof level as in Finnish Patent 70446 mentioned above.
The above-mentioned solutions work very well in principle, but drawbacks have nevertheless been observed especially in connection with large roofs provided with several roof outlets joined to the same tube system. These drawbacks are due to the fact that it is difficult to provide separate roof outlet branches with correct flow resistances. In the event that the separate roof outlet branches cannot be provided with correct flow resistance, the system does not function in the best possible manner, and in the worst case, the system does not function at all. An additional inconvenience is also that tubes in different diameters are available to a relatively restricted extent, and it is therefore often necessary in practice to make compromises when choosing tubes. Further inconveniences are caused by the fact that it has not been possible to regulate the flow resistances of the separate roof outlet branches after the installation of the tube system. It shall be noted that the system is rather sensitive to blockages caused by impurities, so that flaps or the like of whatever kind cannot be used, if a reliable function of the system is desired in all circumstances.